1. Technical Field
The present invention relates generally to semiconductor processing and, more particularly, to chemical-mechanical polishing used to planarize a semiconductor substrate.
2. Related Art
Chemical-mechanical polishing (hereinafter "CMP"), is a common method of planarization used in semiconductor manufacture. CMP typically involves the use of a circular polishing pad, mounted to a polishing table or platen, which is transported and held in contact with the surface of the semiconductor wafer via a carrier. An abrasive slurry, typically water-based, is applied to the surface of the polishing pad to facilitate and enhance polishing of the wafer. During polishing both polishing pad and wafer are rotated relative to one another. As a result, unwanted material is removed from the surface of the wafer, producing a planarized surface.
However, during polishing the surface of the polishing pad becomes matted and unevenly worn. This occurs for several reasons. For example, the pores in the surface of the pad which deliver slurry to the wafer become clogged with slurry and particulate material removed from the wafer. Further, the frictional polishing action designed to planarize the wafer also begins to planarize or wear the pad surface over time. Therefore, one key to effectively employing CMP methods is maintaining the consistency and integrity of the polishing pad surface throughout polishing. This necessitates conditioning the pad surface at frequent intervals to prevent degradation of the polishing pad surface.
Although typical devices used in the industry condition the polishing pad both before and after each wafer polishing cycle, non-uniformities occur within each cycle as a result of the wear discussed above. In addition, the majority of these conditioning techniques and devices are very time consuming, difficult to use and therefore, not cost effective.
In an attempt to remedy the defect, a prior art technique described in U.S. Pat. No. 5,785,585 to Manfredi et al., provides an in-situ conditioning method. Specifically, a stationary wedge-shaped conditioning plate, having a roughened bottom surface, rests flat on the polishing pad surface. Throughout polishing the pad is abraded by the wedge conditioner, thereby providing a consistent and reliable polish for the entirety of each wafer polishing cycle.
Although the method described in Manfredi et al. is quite effective when used with soft pads, such as suba-4, manufactured by Rodel Corporation, it is less effective when used with harder pads, such as IC-1000, by the same manufacturer. In particular, grooves often form in the pad surface, producing reservoirs in which the slurry collects, thereby preventing slurry from reaching the wafer surface. Further, particulate material removed from both the polishing pad and the wafer builds up at the edge of the conditioning plate, thereby interfering with effectiveness of the polishing.
Accordingly, there exists a need in the industry for a simpler, more cost effective apparatus for, and method of, maintaining a consistent polishing surface, for both hard and soft pads, by conditioning the pad throughout the polishing process.